Apparatus for decanning fuel elements



May 7, 1968 FAUGERAS ET AL 3,382,046

APPARATUS FOR DECANNING FUEL ELEMENTS Filed Jan. 17, 1966 2 Sheets-Sheet 1 CAN/V50 FUEL Elf/WENT xxmramz F I G. 1 62 DEC'A/VNED Fl/E L El EMEN7 RI IVG 50L 117/0 ORA/N P/PE 74 May 7, RA ET AL 3,382,046

APPARATUS FOR DECANNING FUEL ELEMENTS Filed Jan. 17, 1966 2 Sheets-Sheet 2 United States Patent ()fiice 3,382,046 Patented May 7, 1968 z 11 Claims. ci. 23-267) This invention relates to a process for decanning fuel elements by continuous chemical process and is also concerned with an apparatus for the practical application of said process.

The solutions which have usually been adopted for the purpose of separating a full or hollow rod of fissionable material from the outer metallic can which surrounds said rod consist in the use of either mechanical processes or chemical processes. The mechanical processes usually consist in shearing the can along generator-lines of this latter, then in mechanically stripping-off the segments which are thus formed. Alternatively, such processes consist in extruding the fuel rod from its can by means of a hydraulic ram. Among other drawbacks, such operations as those referred-to are attended by a danger which is by no means negligible in that chips of fissionable material are liable to be produced either by the cutting tool or by the extrusion ram.

So far as the chemical processes for dissolving cans are concerned, such processes are usually carried out in a discontinuous or batch-feed operation and mainly consist in introducing each fuel element in a container in which said fuel element is in contact with an acid etching solution, in dissolving the can and leaving the fuel element in the container for just the time which is necessary for this operation in order to prevent chemical attack of the fuel rod itself, in rinsing the fuel rod and withdrawing said rod from the container prior to introduction of a fresh fuel element. However, as a rule, such batch processes have a disadvantage in that they result in a substantial volume of effluents. In addition, they call for a large number of operations involving the handling of fuel elements and can therefore permit of only a very moderate throughput.

The present invention is directed to a continuous decanning process which circumvents the above-noted disadvantages in large measure.

This process is characterized in that it consists in continuously circulating said canned fuel elements within a vessel, in dissolving the fuel element cans by contacting with a continuous stream of acid etching solution and then rising the decanned fuel elements prior to their removal from the vessel by means of a continuous circulation of a neutral rinsing solution, the canned fuel elements being circulated in cocurrent flow with the acid etching solution whilst the decanned fuel elements circulate in countercurrent flow to the neutral rinsing solution.

The invention is also concerned with an apparatus for the practical application of the process described above, characterized in that said apparatus comprises in combination a vessel of elongated shape divided into two adjacent chambers which communicate with each other at the ends of said vessel, pipes for introducing at the other end of said vessel on the one hand an acid etching solution which is admitted into the first chamber and on the other hand a neutral rinsing solution which is admitted into the second chamber, a pipe for discharging solutions which opens into said vessel at the end at which the two chambers communicate with each other, means for introducing canned fuel elements into said vessel, means for causing said canned fuel elements to circulate within the first chamber in cocurrent flow with said acid etching solution which effects the decanning of said fuel elements and means for causing said decanned fuel elements to circulate within said second chamber in countercurrent flow to said neutral rinsing solution.

As a preferable arrangement, the means for circulating said canned elements within said first chamber and for circulating said decanned fuel elements within said second chamber consist of two sets of endless screws which rotate in opposite directions.

Aside from the characteristic features noted above, a decanning apparatus in accordance with the invention is endowed with secondary characteristic features which can preferably be employed in conjunction with the preceding but which can if necessary be employed independently thereof. The characteristic features referred-t0 will become more readily apparent from a perusal of the followin" description of one form of embodiment which is given by way of non-limitative example. This description is given in reference to the accompanying drawings, in which:

FIG. 1 represents a longitudinal sectional view of a decanning apparatus as constructed in accordance with the invention.

FIG. 2 represents a sectional view along line I-I of FIG. 1.

FIG. 3 represents a sectional view along line IIII of FIG. 1.

The apparatus which is illustrated in FIG. 1 comprises a first container 4 which is substantially vertical and a vessel 6 which is inclined with respect to the container 4 at an angle of approximately 30. As will be apparent, other relative arrangements of the container 4 and vessel 6 could be contemplated.

The complete apparatus is supported by a metallic frame 7 which is built-up of welded structural beams. The container 4 is closed at the top by a cover 8 which is swingable about a pin 10 Whilst a basket 12 having a crosssection which is practically identical to that of the container 4 is disposed inside said container and placed at the bottom of this latter. Said basket is provided with a perforated base 14 and is designed to recover the solid wastes derived from the more or less complete dissolution of the cans in the apparatus, as will be explained hereinafter. To this end, the basket is fitted with two vertical rods such as the rod 16 which are joined together by means of a ring so as to permit the basket to be lifted and removed from the container 4, these operations being carried out by any suitable means and especially by means of a remotecontrol manipulator.

The vessel 6 is divided approximately at its center into two adjacent chambers, one of said chambers being referred-to as the decanning chamber and the other being referred-to as the rinsing chamber. These two chambers are disposed in parallel relation and separated by a transverse partition Wall 21 of the vessel 6 but communicate with each other at the lower end of the vessel which is thus common to both chambers. At a point of the vessel 6 which is remote from the end at which the two chambers communicate with each other, the chamber 18 is fitted with an inlet pipe 22 for the admission of an acid solution. In addition, said chamber 18 is provided with an outer jacket 24 within which circulates a coolant fluid which can especially be cold water.

The chamber 18 is also equipped with a system for introducing into the vessel 6 fuel elements which have to be decanned by the attacking action of the acid solution, then rinsed prior to removal from the apparatus. This fuelelement feed system consists of a charging unit 26 designed to contain a predetermined number of canned fuel elements 19 which are stacked one above the other as shown in FIG. 1. Said charging unit is placed in position by means of a remote-control manipulator and comprises a vertical shaft 28 and a latch 30 which is placed at the bottom of said shaft, said latch being designed to retain the lowermost fuel element within the charging unit and thus prevent it from falling accidentally into the chamber 18 of the vessel 6. The motion of the latch 30 is controlled by means of a spring 32 by means of a pivotally mounted operating arm 34 (not shown) provided with a stud 36 which is adapted to cooperate with a slot 37 formed in the latch body; prior to positioning of the charging unit 26, the arm 34 is in its top position, thus causing the latch 30 to move forward in such a manner as to obstruct the entrance to the chamber 18. On the other hand, once the charging unit 26 has been placed in position, the latch is thrust back so as to permit the downward motion of the fuel elements and the introduction thereof into the chamber 18, in which said fuel elements are received on a conveyor system and transferred in progressive downward motion while being contacted with the acid etching solution which is fed in through the inlet pipe 22 and which consequently circulates in cocurrent flow with the fuel elements. This downward transfer system consists of two endless screws 38 and 39, the axes of which are parallel to the partition 21 (as shown in FIG. 2) and which rotate in opposite directions while being carried on bearings 40, 42 and 44. The motion of the screw 38 is controlled by a mechanical system 46 which is placed at the top of the chamber 18 and which comprises a pneumatic jack 48 whereby the step-by-step rotation of a ratchet wheel 52 is controlled by means of an arm 50. Said ratchet wheel is keyed on the screw 38 and transmits the movement of rotation thereof to said screw whilst the other screw 39 is driven by means of gears such as the gear which is designated by the reference numeral 54; the gears referred-to are so designed that the movement of the two endless screws 38 and 39 is carried out in opposite directions. Finally, the endless screw 38 is fitted with a cam 56 which acts on a lever 58 so as to partially close off the end of the charging unit 26 while permitting the release of one fuel element 19 per revolution of the screw.

The rinsing chamber 20 is in turn provided with two other endless screws 60 and 61 which serve to lift the fuel elements once these latter have reached the bottom of the chamber 18 in that part of the vessel 6 in which a communication is established with the chamber 20. The motion of the endless screws 38 and 39 is transmitted to the endless screws 60 and 61 by means of one of the gears in such a manner that the screws last mentioned can rotate in opposite directions and that both screws considered together rotate in opposite directions with respect to the screws 38 and 39. The chamber 20 is provided in that portion in which it communicates with the chamber 18 with an inlet pipe 64 for the admission of a neutral rinsing solution, said inlet pipe 64 being substantially at the same level as the pipe 22. The vessel 6 is provided with a single efiluent discharge pipe 66 which opens into the vessel at the base of the two chambers 18 and 20. Said pipe 66 is then connected to a tank 68 which serves to regulate the level of liquid within the two chambers by means of an overflow system and a discharge pipe 69. The chambers 18 and 20 are provided at the bottom of the vessel with a gate 70 for the purpose of withdrawing all the wastes which have collected on completion of an operation and discharging these latter into the basket 12 for subsequent recovery. With this object in view, the container 4 is joined to the vessel 6 by means of a sloping plate 71 which leads directly to the basket 12. Finally, the chamber 20 is provided at the top with an evacuation box 72 for the withdrawal of fuel elements which have passed through the entire apparatus.

The operation of the apparatus can readily be deduced from the foregoing: At the commencement of the operation, the basket 12 is placed at the bottom of the container 4 which is closed by means of the cover 8. The acid etching solution is admitted into the chamber 18 through the pipe 22 whilst the rinsing solution is fed into the chamber 20 through the pipe 64 as well as into the container 4 through a pipe 5. The level is maintained constant within the apparatus by means of the tank 68 which is connected to the pipe 66 for the discharge of efiluents from the vessel 6. Coolant fluid is circulated within the jacket 24 so as to maintain the temperature within the chamber 18 at a sufficiently low value. In both chambers, the acid rinsing solutions therefore flow respectively countercurrent to each other.

The charging unit 26 is placed in position above the chamber 18 and the latch is held in the open position by the arm 34 in the bottom position thereof. The mechanical system 46 which is controlled by the jack 48 causes the screw conveyors 38, 39, 60 and 61 of both chambers to rotate whilst the cam 56 releases one fuel element 19 at each revolution of the screw 38 by producing action on the lever 58.

The fuel elements which are placed on the screw conveyors 38 and 39 are progressively carried towards the base of the decanning chamber 18, the concentration of the acid etching solution being such that the fuel elements reach the lower end of the chamber when the fuel cans are completely dissolved; at this moment, the decanned fuel elements leave the endless screws 38 and 39 and fall onto the endless screws 60 and 61 which, as a result of movements of rotation which are opposite to those of the screws 38 and 39, convey said fuel elements upward through the rinsing solution up to the evacuation box 72, said fuel elements being then directed towards an apparatus for subsequent processing. Within the chambers 18 and 20, the fuel elements which are first in the canned state then decanned therefore circulate in cocurrent flow with the etching solution within the chamber 18 and in countercurrent flow to the neutral rinsing solution within the chamber 20.

The etching and rinsing solutions are continuously replaced and the liquid efiluents are also continuously discharged through the pipe 66 which is connected to the tank 68. The solid wastes which have nevertheless collected at the bottom of the chambers 18 and 20 are periodically discharged through the gate 70 into the basket 12 and the apparatus can be completely emptied after operation by means of an evacuation pipe 74.

When the fuel elements contained in the charging unit 26 have all been processed in a continuous manner, the latch 30 is closed as a result of the lifting of the arm 34 and the charging unit which is removed by the remote manipulator is replaced by a fresh charging unit which is fully loaded with fuel elements. At this moment, the arm 34 is placed in the bottom position and the latch 30 is released once again so as to allow the fuel elements to fall one by one under the action of the cam 56.

The apparatus is constructed of a metal or metal alloy which affords resistance to chemical attack by the acid solution at a predetermined temperature; when it is required in particular to dissolve magnesium cans, the acid solution is a sulphuric acid solution of approximately 5 N, the apparatus being advantageously constructed of steel of the type known as Uranus 50 (registered trademark), the limit of passivity of which is reached at approximately 40 C. In the case of zirconium oxide cans, the etching solution contains a certain proportion of hydrofluoric acid, the apparatus being in that case constructed of steel of the type known as Uranus B 6 (registered trademark).

By way of indication, an apparatus of the type hereinabove described for the purpose of processing magnesiumcanned fuel elements at the rate of one fuel element every two hours has the following dimensions: height, width and depth of the decanning and rinsing chambers respectively equal to 200 cms., 50 cms. and cms.

In order to process a magnesium-canned fuel element 1n an apparatus of this type, a 5 N sulphuric acid solution is utilized and circulated at a flow rate of 2.3 liters per hour, rinsing water being circulated at a flow rate of 2 liters per hour. Experience has proved that, by adopting the above figures, a suitable acidity and temperature gradient is maintained within the decanning chamber in spite of the convection currents which have a tendency to homogenize the solution. At the entrance of the chamber, the hot concentrated acid solution has a strong action on the cans whereas, at the exit of said chamber, the solution which has decreased in concentration and become cold is limited in its action on the rod of fissionable material which is decanned prior to its entry into the rinsing chamber. Under these conditions of operation, the decanning of fifteen fuel elements produces approximately 130 liters of liquid efiluents having an acid concentration which is equivalent to 0.3 N. By way of comparison, batch-type chemical decanning processes produce under the same conditions 210 liters of efi luents having an acid concentration which is equivalent to l N. The flow rate of rinsing water being as hereinabove specified and the decanning chamber being externally cooled by water circulating at 8 C. at a rate of flow of 150 liters per hour, the resulting mean temperature of the acid bath is of the order of 29 C., which is below the limit of passivity of a steel of the Uranus 50 type.

In order to limit the number of fuel elements which are present in the apparatus, the speed of rotation of the rinsing chamber conveyor screws is a multiple of the speed of rotation of the decanning chamber screws, which accordingly makes it possible to shorten the rinsing time. Moreover, in order to prevent the formation of an explosive air-hydrogen mixture which results from the attacking action of the acid solution on the fuel can, that section of the apparatus which is located above the decanning chamber is advantageously ventilated and put under reduced pressure. Finally, by blowing air into the section located above the rinsing chamber, there cannot take place any gas transfer from the decanning chamber to the rinsing chamber.

Once the feed rates of the different solutions have been determined, the apparatus can operate in a continuous manner without any subsequent adjustment and produces rapid dissolution of cans while providing a volume of effluents which is lower than that which is produced by systems which entail the application of batchfeed processes.

As will be readily understood, the invention is not limited to the form of embodiment which has been described and illustrated and which has been given solely by way of example.

What we claim is:

1. Decanning apparatus comprising an inclined vessel of elongated shape, two adjacent parallel chambers set one above the other in said vessel communicating with each other at the lower end of said vessel, a feed-in pipe in the upper end of the upper chamber for an acid etching solution admitted into the upper of said chambers and a feed-in the pipe in the upper end of the lower chamber for admitting a neutral rinsing solution into the lower of said chambers, a pipe for discharging solutions opening into the lower end of said vessel at which said two chambers communicate, means for introducing canned fuel elements into the upper end of said upper chamber, screw conveyor means within and extending the length of the upper chamber for conveying said canned fuel elements downwardly within said upper chamber in concurrent flow with said acid etching solution for decanning said fuel elements, screw conveyor means within and extending the length of the lower chamber for conveying the decanned fuel elements upwardly within the lower chamber in counter-current flow to said neutral rinsing solution and outlet means in the upper part of the lower chamber for removing the decanned fuel elements, said means for introducing said canned fuel elements into the upper end of said upper chamber comprising a removable charging unit, a passageway in said unit for downward admission of said fuel elements opened at the lower end thereof into said chamber, a latch near the lower end of said passageway removably retaining said fuel elements, a lever closing off the lower end of said passageway and a cam member actuating said lever attached to the shaft of the screw conveyor in the upper chamber to introduce into said upper chamber a canned fuel element for each full revolution of said screw.

2. Decanning apparatus as described in claim 1, including an operating arm actuating said latch, a pin on said arm forming an eccentric stud slidable in a groove in said latch and a control spring opposing the motion of said arm and continuously urging said latch toward fuel element retaining position.

3. Decanning apparatus as described in claim 1, said member controlling the position of said lever consisting of a cam keyed to one of said endless screws whereby one of said fuel elements is introduced into the first of said chambers for each full revolution of said one of said endless screws.

4. Decanning apparatus as described in claim 1, including a box for the second of said chambers receiving said decanned fuel elements after rinsing.

5. Decanning apparatus as described in claim 1, including a gate at the end of said vessel at which said two chambers communicate for discharging from said vessel solid Waste derived from the decanning operation.

6. Decanning apparatus as described in claim 5', including a vertical container connected to said vessel at the end of said vessel at which said two chambers communicate and a removable basket in said container for collecting the solid waste discharged through said gate.

7. Decanning apparatus as described in claim 6, including integral handling rods for said removable basket for withdrawal of said basket through a cover closing the top of said container.

8. Decanning apparatus as described in claim 6, the axis of said container and the axis of said vessel making an angle of approximately 30 with respect to each other.

9. Decanning apparatus as described in claim 6, including an evacuation pipe connected to said container at its base.

10. Decanning apparatus as described in claim 1 including an outer jacket for said upper chamber for the circulating of a cooling fluid.

11. Decanning apparatus as described in claim 1 including a tank, said pipe for discharging solutions being connected to said tank and an overflow outlet for said tank regulating the level of said solutions within said chambers.

References Cited UNITED STATES PATENTS 799,824 9/1905 Baenen 134-65 1,960,692 8/1929 Brown 134-65 2,308,883 1/1943 Kettenback 134-65 X 2,612,178 9/1952 Skinner l34132 2,934,414 4/1960 Bradley 23270 X 3,165,377 l/l965 Katz 23-324 3,268,303 8/ 1966 Ramaswami 23324 3,303,004 2/1966 Bennett 23-324 NORMAN YUDKOFF, Primary Examiner.

CARL D. QUARFORTH, Examiner. S. TRAUB, S. EMERY, Assistant Examiners. 

1. DECANNING APPARATUS COMPRISING AN INCLINED VESSEL OF ELONGATED SHAPE, TWO ADJACENT PARALLEL CHAMBERS SET ONE ABOVE THE OTHER IN SAID VESSEL COMMUNICATING WITH EACH OTHER AT THE LOWER END OF SAID VESSEL, A FEED-IN PIPE IN THE UPPER END OF THE UPPER CHAMBER FOR AN ACID ETCHING SOLUTION ADMITTED INTO THE UPPER OF SAID CHAMBERS AND A FEED-IN THE PIPE IN THE UPPER END OF THE LOWER CHAMBER FOR ADMITTING A NEUTRAL RINSING SOLUTION INTO THE LOWER OF SAID CHAMBERS, A PIPE FOR DISCHARGING SOLUTIONS OPENING INTO THE LOWER END OF SAID VESSEL AT WHICH SAID TWO CHAMBERS COMMUNICATE, MEANS FOR INTRODUCING CANNED FUEL ELEMENTS INTO THE UPPER END OF SAID UPPER CHAMBER, SCREW CONVEYOR MEANS WITHIN AND EXTENDING THE LENGTH OF THE UPPER CHAMBER FOR CONVEYING SAID CANNED FUEL ELEMENTS DOWNWARDLY WITHIN SAID UPER CHAMBER IN CONCURRENT FLOW WITH SAID ACID ETCHING SOLUTION FOR DECANNING SAID FUEL ELEMENTS, SCREW CONVEYOR MEANS WITHIN AND EXTENDING THE LENGTH OF THE LOWER CHAMBER FOR CONVEYING THE DECANNED FUEL ELEMENTS UPWARDLY WITHIN THE LOWER CHAMBER IN COUNTER-CURRENT FLOW TO SAID NEUTRAL RINSING 